With recent developments in semiconductor technology, considerable improvements have been made in the area of controlling the on-off operation of indicator devices such as navigational flashing lights and fog horns. Semiconductor logic circuitry is quite suitable for such implementation since, due to its small size, it can serve to reduce the overall size and weight necessary for each individual indicator unit. This can be especially significant with regard to flashing navigational lamps since a large number of such units are often used. Also, because of the relatively low power consumption of semiconductor devices, the units can be utilized in remote locations where only battery power is feasible. Further, semiconductor logic circuitry is generally quite reliable, which is also of utmost importance with regard to remote locations where servicing can be difficult.
In particular, the development of semiconductor techniques has led to a number of units for signalling with navigational lights utilizing programmable control means. Examples of such systems are U.S. Pat. Nos. 4,124,842; 4,029,994; 4,024,491; 3,810,150; and 3,781,853. These various patents teach systems which can provide desired signalling such as Morse Code signalling utilizing only battery power. Therefore, these systems are suitable for remote usage.
Notwithstanding such developments, a number of problems still exist in this area. In particular, the question of choosing a suitable programmable unit must be dealt with. This question leads to the necessity of making choices between units which each have their own drawbacks.
For example, one type of currently popular programmable unit which can be used in such systems is a programmable read-only memory (hereinafter referred to as a "PROM"). These units are generally programmed in advance with desired codes for the various flashing sequences desired, and then utilized with a suitable addressing circuit for selecting appropriate code words and passing these to the indicator devices for controlling the on-off operation thereof. Typically, the PROMs are either CMOS (complementary metal-oxide semiconductors) or TTL (transistor-transistor-logic). A number of commercially available models of each are presently available. However, before a choice is made in constructing a control system, the relative advantages and disadvantages of each must be considered.
With regard to this choice, it must be noted in the first place that the number of CMOS-PROMs currently available is much less than the number of TTL-PROMs. Alto, the CMOS units are more expensive. Besides this, the CMOS-PROMs are more sensitive to handling and are, in general, less stable than their TTL counterparts. However, the CMOS-PROMs have one very large advantage over the TTL-PROMs. This advantage is a considerably lower power consumption requirement. The drawback of the relatively high power required by a TTL-PROM presents a significant problem in remote location navigational indicators since the TTL-PROMs can rapidly drain the limited battery power available.